It works, but most owners opt for something better, or at least perceived to be better. The ready brake is a surge-operated system and in the past these have been somewhat less than optimal. Perhaps the surge mechanism technology has improved in recent years but in the past the mechanism has been subject to mechanical wear and corrosion and may not work well over time or require cleaning, lubrication and adjustment. Of course, that can be said of most anything if you want it to stay in good operating condition, but the other systems do not have their mechanisms so exposed to whether, road dirt, etc.
U-Haul uses surge breaks on their trailers so they don't have to wire brake systems into the renter's vehicle, but they also maintain the trailers regularly and professionally. Private owners tent to use the stuff and forget them.
